Add tiny Makefile for building virtme-ng-init

This is primarily just a small convenience for building an updated
virtme-ng-init when running vng from the source directory.  In order
to keep the definition of "how to build init" in one place, also
update setup.py to run 'make' instead of directly invoking 'cargo'.

Signed-off-by: Zev Weiss <zev@bewilderbeest.net>

Author: zevweiss

Makefile

@@ -0,0 +1,3 @@
+.PHONY: init
+init:
+	cd virtme_ng_init && cargo install --path . --root ../virtme/guest

setup.py

@@ -59,10 +59,7 @@ def run(self):
         print(f"BUILD_VIRTME_NG_INIT: {build_virtme_ng_init}")
         # Build virtme-ng-init
         if build_virtme_ng_init:
-            check_call(
-                ["cargo", "install", "--path", ".", "--root", "../virtme/guest"],
-                cwd="virtme_ng_init",
-            )
+            check_call(["make", "init"])
             check_call(
                 ["strip", "-s", "../virtme/guest/bin/virtme-ng-init"],
                 cwd="virtme_ng_init",